1. Field of the Invention
This invention relates to a shaft position sensor used to measure the dimensions of the shape of an object or to sense the displacement of the object.
2. Description of the Related Art
Generally, a shaft position sensor is used to measure the length and dimensions of an object or to sense the displacement of the object. Such as shaft position sensor, is (mentioned in the unexamined publication of Japanese Utility Model Application, No. 65904/1991) by the present inventor.
The above described shaft position sensor shall be explained with reference to the drawings. FIG. 17 is a vertically sectioned view showing the structure of a conventional shaft position sensor.
As shown in FIG. 17, a shaft position sensor 1 is provided with a housing 2 which is provided in the bottom with a shank 2a integrally connected with the housing 2. The shank 2a comprises a cylindrical member projecting outward of the housing 2 coaxially with the axis of the housing 2. A screw part 2b is formed at the tip of the shank 2a. A groove 2c extending in the axial direction of the shank 2a is formed in the outer peripheral part of the shank 2a.
A measuring shaft 3 is contained within the housing 2, and comprises a shaft member extending coaxial 1y with the axis of the housing 2, projects at the tip out of the housing 2 through the shank 2a and is provided at the tip with a contactor 4 to be in contact with an object to be measured.
The measuring shaft 3 is fitted with an insulatable rectangular parallelepiped movable body 5 which is provided with a hole 5a extending coaxially with the axis of the measuring shaft 3. The measuring shaft 3 is inserted through the hole 5a. A hole 5b extending coaxially with the axis of the hole 5a is provided in the peripheral part of the hole 5a of the movable body 5.
A ring-like fixed contact member 6 is fitted in an opening on one side of the hole 5b of the movable body 5 and a ring-like fixed contact member 7 is fitted in an opening on the other side of the hole 5b. The respective fixed contact members 6 and 7 are electroconductive and have lead wires 8 and 9 respectively connected to them. The respective lead wires 8 and 9 are bundled into one bundle and are then led out of the housing 2 as a connecting line 10.
Two spherical movable contact members 11 and 12 are respectively movably inserted into the hole 5b of the movable body 5. A spring member 13 is arranged between the movable contact members 11 and 12 and comprises an electroconductive spring member. The movable contact member 11 is pressed against the fixed contact member 6 by the spring force of the spring member 13 and the movable contact member 12 is pressed against the fixed contact member 7 by the spring force of the spring member 13. The movable contact member 11 constitutes a first switching means in cooperation with the fixed contact member 6 and the movable contact member 12 constitutes a second switching means in cooperation with the fixed contact member 7.
A spring member 14 is arranged between the movable body 5 and the upper part of the housing 2. The spring member 14 presses the movable body 5 toward the lower part of the housing 2 with its spring force.
The housing 2 is fitted with a push pin 15 for adjusting the contact position of the movable contact member 11 and fixed contact member 6 and a push pin 16 for adjusting the contact position of the movable contact member 12 and fixed contact member 7. The push pin 15 is provided in the bottom of the housing 2 so that its tip may be opposed to the movable contact member 11. An insulating member 17 is inserted between the push pin 15 and the bottom of the housing 2.
On the other hand, the push pin 16 is screwed into a screw hole (not illustrated) provided in the upper part of the housing 2. The displacement of the tip of the push pin 16 is regulated with the screwing of the push pin 16 with the above mentioned screw hole. The push pin 16 is made of an insulating member and is provided with a grip 16a for making its rotating operation easy. The displacement of the push pin 16 is set so as to adjust the signal generating point for the displacement of the measuring shaft 3.
A guide member 18 is fitted to the bottom of the housing 2 and comprises a member rising on the axis within the housing 2 and slidably fitted in a groove (not illustrated) formed on the side surface of the movable body 5.
A bracket 19 for holding the housing 2 with a supporter (not illustrated) of an outside device is fitted to the shank 2a of the housing 2 and is provided at the end with a hole 19a for receiving the shank 2a and a screw hole 19b communicating with the hole 19a and extending in the direction intersecting at right angles with the axis of the hole 19a.
A spring member 20 is held between the bracket 19 and the bottom of the housing 2. A nut 21 is screwed to the screw part 2b of the shank 2a.
A bolt 22 is screwed in the screw hole 19b of the bracket 19 and is positioned at the tip within the groove 2c of the shank 2a.
Now, the operation of the above described shaft position sensor 1 shall be explained with reference to the drawings. FIG. 18 is a view showing the first operating state of the shaft position sensor of FIG. 17. FIG. 19 is a view showing the second operating state of the shaft position sensor in FIG. 17.
First of all, as shown in FIG. 17, the bracket 19 of the shaft position sensor 1 is fixed to the supporter. Then, the adjusting operation before starting the measurement is made. This adjusting operation includes the adjustment of the distance between the tip of push pin 15 and the movable contact member 11 and the adjustment of the distance between the tip of the push pin 16 and the movable contact member 12. In the adjustment of the distance between the tip of push pin 15 and the movable contact member 11, the nut 21 is rotated after the conductor 4 is contacted with a guage(not illustrated) having a reference dimension of a lower limit. As the tip of the bolt 22 is positioned within the groove 2c of the shank 2a, with the rotation of the nut 21, the shank 2a, that is to say, the push pin 15 will be moved in the axial direction of the measuring shaft 3 and the contact position of the fixed contact member 6 with the movable member 11 will be found. The first position in which the fixed contact member 6 and the movable contact member 11 are separated from each other will be regulated by this distance adjustment.
In the adjustment of the distance between the tip of the push pin 16 and the movable contact member 12, after the contactor 4 is contacted with the gauge (not illustrated) having a reference dimension of an upper limit, the grip 16a of the push pin 16 is rotated and the distance between the tip of the push pin 16 and the movable contact member 12 is adjusted, that is to say, the contact position of the fixed contact member 7 with the movable contact member 12 will be found.
The measurement is started after the adjusting operation before starting the measurement is completed. When the measurement is started, that is to say, when the object to be measured and the contactor 4 are separated from each other, as shown in FIG. 17, the movable contact member 11 will be in contact with the push pin 15 and the movable contact member 11 and the fixed contact member 6 will be separated from each other. On the other hand, the movable contact member 12 will be in contact with the fixed contact member 7 by the spring force of the spring member 13 and therefore an open circuit will be formed between the lead wires 8 and 9 through the movable contact member 11, the spring member 13, the movable contact member 12 and the fixed contact member 7 from the fixed contact member 6.
Then, when the object to be measured relatively approaches the contactor 4 in the axial direction of the measuring shaft 3, the object and the contactor 4 will contact with each other. By the contact of the contactor 4 with the object to be measured, as shown in FIG. 18, the measuring shaft 3 will be pushed up together with the movable body 5 toward the upper part of the housing 2. With the movement of the movable body 5, the fixed contact member 6 will be moved toward the movable contact member 11. When the measuring shaft 3 reaches the first measuring position, the fixed contact member 6 and movable contact member 11 will be in contact with each other while the fixed contact member 7 and movable contact member 12 are held in contact with each other, that is to say, the first switching means will operate to close. Therefore, a closed circuit will be formed between the lead wires 8 and 9 through the movable contact member 11, the spring member 13, the movable contact member 12 and the fixed contact member 7 from the fixed contact member 6.
Further, when the measuring shaft 3 is pushed up to the second measuring position by the object to be measured, as shown in FIG. 19, the movable contact member 12 and the tip of the push pin 16 will be in contact with each other and the movement of the movable contact member 12 together with the measuring shaft 3 will be regulated. At the same time as the measuring shaft 3 exceeds the second measuring position, the movable contact member 12 will separate from the fixed contact member 7, that is to say, the second switching means will operate to open. Therefore, an open circuit will be formed between the lead wires 8 and 9 through the movable contact member 11, the spring member 13, the movable contact member 12 and the fixed contact member 7 from the fixed contact member 6.
In the above, when the measuring shaft 3 is pushed into the housing 2, a closed circuit will be formed in the first position and an open circuit will be formed in the second position.
However, because the fixed contact member 6, the movable contact member 11, the spring member 13, the movable contact member 12 and the fixed contact member 7 are arranged in parallel and series with the measuring shaft 3, the length in the vertical direction of the housing 2 will become so large that, when a large force is applied to the housing 2, a large moment will be generated in the bracket fitting position of the shank 2a. As a result, such position of the housing as the shank 2a will be likely to be damaged. In adjusting the measuring range, when the first position is adjusted by rotating the nut 21 and when the second position is adjusted by the push pin 16, as the position of operating the adjustment is divided into the upper part and lower part, the operation of adjusting the measuring range will be a trouble.